1. Field of the Invention
The present invention relates to an anticorrosive gypsum composition which is highly anticorrosive when in contact with metal. The invention can be applied to various gypsum products, especially to anticorrosive gypsum boards, anticorrosive gypsum plasters and the like.
2. Description of the Prior Art
Heretofore, in addition to being an important inorganic raw material, hardened gypsum has been used for gypsum board and gypsum plaster, etc. because of its high strength. However, it has been found that gypsum suffers from the disadvantage of being corrosive to metals such as mild steel when in contact with them. This is due to the acidic property of gypsum itself or to the small amount of residual phosphoric acid found in gypsum formed as a by-product in the preparation of phosphoric acid. In order to overcome this disadvantage in the past, anticorrosive processing of the metal surface or use of expensive noncorrosive metals have been employed. For example, iron nails cannot be used in conjunction with gypsum board for construction because of the corrosive action of the gypsum. Accordingly, it has been necessary to use zinc coated iron nails or stainless steel nails. Moreover, when gypsum plaster is used in making a wall surface, iron products hung on the wall, such as iron nails, when in contact with the gypsum plaster can be disadvantageously corroded. Once again, in order to overcome this disadvantage, noncorrosive metals have been obligatory. It would be most desirable to have a gypsum composition which is not corrosive to metals with which it is in contact.